1. Field of the Invention
The present invention relates to an external antenna which transmits data to and receives data from a non-contact integrated circuit (hereinafter sometimes referred to as “non-contact IC”) placed within a case. This application is based on Japanese Patent Application No. 2003-099621 filed on Apr. 2, 2003, and the content of which is incorporated by reference.
2. Description of the Prior Art
In recent years, various products to which a non-contact IC (integrated circuit) is applied have been put into a market. As an example, a magnetic tape cartridge having a cartridge memory with a non-contact IC built therein can be mentioned. Information within the cartridge memory provided within the magnetic tape cartridge is used in various external apparatuses such as a tape drive and a robot hand within a library and, thus, techniques which make it possible to be accessed with the tape cartridge memory in a multi-direction have hitherto been developed.
As such techniques, a technique has been known in which a rectangular cartridge memory wherein a loop-shaped antenna (hereinafter referred to as “loop antenna”) is formed on the outer circumference is slanted 45° relative to the bottom surface or where two sides of the loop antenna approach two sides of the cartridge case by slanting the loop antenna 45° relative to the bottom surface (for example, see Japanese Patent Laid-Open No. 2002-140879, and Japanese Patent Laid-Open No. 11-339436). In such a technique, the data is exchanged by a loop shaped external antenna provided on a flat portion of an external device coming close to either of the two sides of the tape cartridge.
However, in the prior art techniques, since only one side of the loop antenna in the external antenna contributes to transmission/receiving with the loop antenna formed on the cartridge memory, it has been difficult to make communication quality good. Specifically, as shown in FIG. 7, at a portion near one side 61 of a substantially rectangular loop antenna 6, which is an-external antenna, a magnetic field becomes parallel to a cartridge memory CM, which is diagonally placed, making it difficult to obtain binding of the magnetic field, as a result, communication cannot be performed. On the other hand, at a portion opposite one side 62 (Range A in the figure), the magnetic field becomes perpendicular to the cartridge memory CM, binding of the magnetic field required for communication can be obtained, and thus, only the side 62 contributed to transmission/receive to the cartridge memory CM in the conventional techniques. For this reason, when such a plane type loop antenna 6, which is the external antenna, is used, the position of transmission/receiving with the cartridge memory CM is restricted, and there is also the problem that the efficiency is reduced by half. Particularly, when being communicated with a magnetic tape cartridge memory in the state where a magnetic tape cartridge is accommodated within a housing case, since a distance between the external antenna and the cartridge memory becomes large, the communication quality thereof has been desired to be enhanced.
An object of the present invention is to provide an external antenna which can enhance communication with a cartridge memory diagonally placed within a magnetic tape cartridge.